On the Centennial of the Academic Careers (1919–2019) of Llewellyn M. K. Boelter and William H. McAdams: American Pioneers in Heat and Mass Transfer

The narrative in this paper is in principle based on the generally accepted notion that heat transfer primarily consists of three basic modes: conduction, convection, and radiation. Even though “heat” and “thermal processes” have roots in antiquity [1–4], the modern development of heat transfer can perhaps be dated back to 1701, when Isaac Newton, working on thermometry, suggested a constitutive relationship that is often now referred to as the “Law of Cooling” [5]. In a commentary on the antecedents of the developments in heat transfer from Newton to Eckert (1700–1960), Cheng and Fujii [6,7] have identified several milestones. A partial list of these earlier developments in the broad spectrum of the field, encompassing fluid dynamics and heat transfer in the 18th and 19th centuries, includes the following:

• 1701—Newton's “Law of Cooling”

• 1783—Bernoulli's theorem

• 1812—Fourier's analytical theory of heat

• 1812—Navier-Stokes equations

• 1840—Hagen–Poiseuille flow

• 1879—Reynolds number

• 1890—Couette flow

• 1894—Reynolds equations for turbulent flow

Contextualizing this evolution to contemporary times in 1988, as part of the celebration of the half-century of heat transfer activity of the American Society of Mechanical Engineers (ASME), Edwin T. Layton, Jr. and John H. Lienhard [8] published a very important compilation entitled: History of Heat Transfer: Essays in Honor of the 50th Anniversary of the ASME Heat Transfer Division. This Layton–Lienhard volume also includes their recounting of the History of the ASME Heat Transfer Division (from the formation as the ASME Heat Transfer Professional Group in 1938, which became an ASME Division in 1941, spanning 50 years till 1988) along with eleven other contributions. All of these historical reports provide insightful accounts of the development and growth of heat transfer in the U.S. It should be noted that the advancements to the field were not limited to mechanical engineers. In fact, early on, many ground-breaking contributions to the growth of the broad area of heat transfer in the U.S. also came from chemical engineers. A case in point is the seminal work of Hoyt C. Hottel in radiation and combustion heat transfer [9].

Starting in the late 1800s through the first part of 20th Century, there was an increasing interest in heat transfer developments in Europe, especially in Germany. Some notable contributors from this period, which was arguably the foundational golden era of the field, include the following:

• Max Planck (1858–1947): Quantum Theory, Thermal Radiation

• Ludwig Prandtl (1875–1953): Boundary Layer Phenomena

• Max Jacob (1879–1955): Heat Transfer with Phase Change

• Theodore von Karman (1881–1963): Integral Analysis of Boundary Layers; Analogy between Heat and Momentum Transfer

• Wilhelm Nusselt (1882–1957): Condensation, Dimensionless Analysis

• Ernst Schmidt (1892–1975): Analogy between Heat and Mass Transfer

• Ernst R. G. Eckert (1904–2004): Rocket and Jet Engine Science

Many other engineers, scientists, and technicians have since made significant seminal advancements to the art and science of heat (and mass) transfer, including fluid dynamics [7]. More importantly, several of the above-listed pioneers moved to the U.S. and continued their work to establish strong heat and mass transfer programs in this country. Professor Theodore von Karman left Germany in 1930 to join the California Institute of Technology (Caltech) as the Director of the Guggenheim Aeronautical Laboratory (GALCIT), and then later founded and became the first Director of the Jet Propulsion Laboratory (JPL) in Pasadena, California. Likewise, both Max Jakob and Ernst Eckert immigrated from Europe, respectively, in 1936 and 1945. While Jakob took up a faculty position at the Illinois Institute of Technology (IIT), Chicago, IL (formerly the Armor Institute of Technology), Eckert first joined the Wright–Patterson Air Force Laboratory, OH, and subsequently the University of Minnesota—Twin Cities, MN. An interesting development in this postwar period was that George A. Hawkins, who later became Dean of Engineering at Purdue University, West Lafayette, IN, had attended Jakob's graduate-level heat transfer lectures at IIT. This learning lineage and his own initiative ultimately played a major role in the establishment of a very strong heat transfer program in Mechanical Engineering at Purdue University.

Fortuitously in the 1890s, the U.S. had the largest chemical industry in the world with a strong geographical concentration in the Mid-Atlantic States. The city of Wilmington, DE, in the Delaware Valley, alone was home to Atlas Powder Company, Hercules Powder Company, and E.I. Dupont de-Nemours and Company (DuPont). This provided an enticing environment for many engineering researchers of that era to make seminal advancements as they blended theory and practice in their research while in academia. In fact, many of them spent considerable time in industry before accepting academic positions at institutions such as the Massachusetts Institute of Technology (MIT) and the University of Delaware. A classic and enduring example is that of Dr. Allan P. Colburn (1904–1955), who after spending about 10 years working for DuPont joined the University of Delaware as a professor in Chemical Engineering in 1938. However, while still at DuPont and working on flow of fluids, distillation, and absorption, among others, he published a paper in 1933 [10] in which he introduced the “Colburn Analogy” and the dimensionless heat transfer j-factor that is now ubiquitous for characterizing compact heat exchangers [11]. It may be noted that some of this work at DuPont was in collaboration with his colleague Thomas H. Chilton, and the friction loss—heat transfer relationship was extended to estimate mass transfer coefficients that are now referred to as the Chilton–Colburn analogy [12]. To this day, the University of Delaware has one of the strongest Chemical Engineering programs in the U.S.

The American Society of Mechanical Engineers (ASME) was founded in 1880, and its first president was Robert Henry Thurston (1839–1903). In his youth, Thurston had worked at his father's manufacturing shops and had first-hand experience in the construction of steam engines, boilers, and general power plants. After a 20-year stint as a faculty member at the U.S. Naval Academy and Stevens Institute of Technology, he moved to Cornell University in 1885 as director of the Sibley College [13]. In the ensuing 18 years in this capacity, Thurston reorganized it as a College of Mechanical Engineering with emphasis on scientific classroom instruction accompanied by substantive laboratory testing. Just as the case with Colburn, the work that Thurston did was yet another case of synergy between engineering practice and academic advancement in that era in the evolving history of heat transfer in the U.S. The publication of the Transactions of the ASME began the same year ASME was founded (1880); however, during the first 32 years, only 8 papers dealt with heat transfer [8]! The topically dedicated ASME Journal of Heat Transfer (renamed in 2023 as ASME Journal of Heat and Mass Transfer) did not come into being until much later with the first publication in 1959². These were the formative years and while there was growing interest and associated engineering science activity in heat transfer in the U.S. in the late 1800s and early 1900s, the rapid progress in Europe at that time easily overshadowed these efforts.

It was with this backdrop and at the start of the 20th century that the development of heat transfer in the U.S. saw a remarkably dramatic change. The subject area of heat and mass transfer began to be formalized for college curricula and classroom instruction, driven by industrial needs and the concomitant academic preparedness. In this paper, we attempt to weave a story wherein the pioneering work of both chemical and mechanical engineers played a major role in the development and growth of the field of heat (and mass) transfer in the U.S.

While many individuals and institutions have played important roles [7,14,15], the two most prominent trailblazers in this effort and perhaps the key players were: William Henry McAdams (1892–1975; Chemical Engineering or ChE; see photo in Fig. 1), and Llewellyn Michael Kraus Boelter (1898–1966; Mechanical Engineering or ME; see photo in Fig. 2). They both began their career in academia in 1919, where one (McAdams) was on the east coast in Massachusetts and the other (Boelter) was on the west coast in California. Both were born in the central part of U.S., where they also spent their childhood schooling days, and neither had an earned doctorate degree! In many ways, they set the stage for formal learning of and curricula for heat and mass transfer in both graduate and undergraduate university education with their books [16–18] and lecture notes [19]. These contributions later became the incipient resources for further expansion of the field with classics authored most notably by Jakob [20,21], Eckert [22–24], Kern [25], Kreith [26], Bird et al. [27], and Rohsenow and Choi [28], among others, which are still widely used references in both academic and industrial circles. The formative paths that McAdams and Boelter concurrently charted indeed became a foundational basis for the development and growth of heat-mass transfer not only in the U.S. but throughout the world.

Born in Cynthiana, Kentucky, on March 15, 1892, William H. McAdams initially attended Transylvania College and then transferred to the University of Kentucky. From the latter institution, he went on to receive BS and MS degrees in Industrial Chemistry, respectively, in 1913 and 1914. Subsequently, he joined MIT where he received an MS degree in Chemical Engineering in 1917. After a year as a Chemical Engineer with the Goodyear Tire and Rubber Company, he worked to support the Chemical Warfare Service during World War I as a Captain Assistant Chief of the Development Division [9]. Then in 1919, he joined the MIT faculty as an Assistant Professor of Chemical Engineering. For the next four decades, he continued at this institution and had an eminently distinguished career with extensive engagement in classroom teaching, research, scholarly publications, and participation in a variety of professional activities including consulting. The presence of outstanding faculty in Chemical Engineering at MIT during this period, notably Warren K. Lewis, William H. Walker, Walter Whitman, George E. Davis, Thomas K. Sherwood, Hoyt C. Hottel, Edwin R. Gilliland, and others, undoubtedly provided a professional environment in which McAdams was challenged and motivated to achieve even greater heights.

It is well documented that MIT was the first U.S. College to offer an undergraduate four-year curriculum in Chemical Engineering. However, initially, when such a program was established in 1888 [9], it was organized as part of the Chemistry Department. Several faculty members including Warren Lewis had very strong feelings about this situation, preferring a greater distinction between Chemistry and Chemical Engineering. In late 1919 and early 1920, Warren Lewis recognized that an education in chemical engineering needed a more unified approach. He thus worked with several MIT faculty members, including McAdams, and undertook a major effort to separate chemical engineering from chemistry. As a result of this joint effort, the Department of Chemical Engineering was formally established as an autonomous and separate discipline entity in 1920 at MIT [9].

In 1923, William H. Walker, Warren K. Lewis, and William H. McAdams published the first edition of a book entitled Principles of Chemical Engineering [29] that was used to teach undergraduate chemical engineering students. This book and its two later editions, in 1927 [30] and 1937 [31], resulted in the foundation of a very strong chemical engineering program at MIT. The 1st edition of this book was divided into the following five parts to essentially cover the primary activities in the field at that time:

• Principles of Stoichiometry

• Heat Transfer and Fluid Mechanics

• Fuels and Combustion

• Crushing and Grinding

• Evaporation and Distillation

The practical applications of these five parts helped to meet the needs of the prevalent process industries in the early 1920s. The goal of these foundational authors, in which McAdams played a major role, was to establish Chemical Engineering as an important, separate, and distinct discipline, with a curriculum that had fundamental content of value to not only advanced students and researchers but also practicing engineers and manufacturers as well, for which this book eminently fulfilled the purpose.

This ground-breaking tome was revised four years later by the same set of authors (Walker, Lewis, and McAdams) with the publication of the 2nd edition of Principles of Chemical Engineering in 1927 [30]. Unfortunately, Professor Walker, who was originally the leader of this effort, died in an automobile accident in 1934 [9]. Edwin R. Gilliland eminently stepped in as the fourth author at the time for the publication of the 3rd edition of this seminal book by the original “triad” in 1937 [31], and Walker's name was retained as an author in recognition of his earlier foundational work. However, Professors McAdams and Gilliland did most of the work in the production of this edition [31], which was the last in its history. The chapter on fluid flow and heat transfer was in fact completely rewritten in the 3rd edition to include the latest developments in the field with more focus on the phenomena involved and quantitative modeling. That the book is intrinsically tied to heat and mass transfer is evident from some of the topical chapters (heat transfer and fluid mechanics, fuels and combustion, evaporation, and distillation).

A book review in 1937 [32], while acknowledging the contribution of the fourth author Gilliland and the considerable useful revisions, stated “… This is one of the excellent standard texts on chemical engineering principles.” Likewise, in the following year, D. B. Keyes went on to comment in his review [33]: “… This book by Walker, Lewis, McAdams, and Gilliland, Principles of Chemical Engineering, is unquestionably the best in its field ….” This book and its three editions [29–31] unquestionably played a leading role in firmly establishing Chemical Engineering as a major engineering discipline, not only at MIT but perhaps worldwide. It integrated the naturally inherent connection of heat and mass transfer to chemical engineering science and equipment design and made a lasting contribution to both research and industrial practice.

Furthermore, as a concurrent work in this same period, McAdams formalized the subject matter of heat transfer and published in 1933 the 1st edition of his now classic book entitled: Heat Transmission [16]; see Fig. 3 for an image of its 2nd edition. This work was sponsored by the Committee on Heat Transfer of the National Research Council, with the offer of additional funds by ASME. After all, in that time period, the U.S. was in the middle of the Great Depression [34] and money was scarce; nevertheless, the additional funds were not needed. McAdams's book went through three editions (1933, 1942, and 1954) [16–18] and sold over 50,000 copies, which is an unbelievable total for a technical book. In his review of the 3rd edition of Heat Transmission (1954), George A. Hawkins of Purdue University commented [35]: “The third edition of this outstanding textbook and reference book reflects the progress made in the area of heat transmission since the publication of its predecessor 12 years ago … … This is an authoritative treatment of the field of heat transfer and is highly recommended for engineers and scientists ….” The enduring impact of this work is perhaps eminently reflected in another 2004 book (1985 reprint) purchaser's review comments³: “… Even though 50 years have elapsed since its 3rd edition, the book still remains a valuable source of information ….”

The Heat Transmission book by McAdams was not only seminal as a comprehensive subject resource but was lastingly transformative for two important reasons. First, the timing of its publication was propitious in providing the much-needed compendium for promotion and development of heat transfer research and education in both U.S. and across the globe. Second, when published in 1933, it was the first heat transfer textbook written in English and in many ways served as a template for the many textbooks to follow. The subject contents in the book were distributed in the following 11 chapters:

• Introduction

• Conduction

• Heating and Cooling of Solids

• Radiation of Heat

• Dimensional Analysis

• Flow of Fluids

• Introduction to Convection

• Fluids inside Pipes

• Fluid outside Pipe Sensing Vapors

• Heat Transfer in Boiling Liquids

In all three editions of Heat Transmission [16–18], McAdams used many graphs, tables, and references to present his information. Thus, this material was valuable to engineering practitioners as well as undergraduate and graduate students.

Note that the friction factor f is an inverse function only of the Reynolds number Re. This relation was developed based on experimental data in 1932, and after 101 years it is still used as a simple way to predict turbulent pressure drop inside circular tubes. Similarly, the early exploration of flow boiling by McAdams and colleagues [41], wherein effects of water flow velocity, subcooling, pressure, and dissolved air, among others, on the heat transfer performance, was a seminal precursor to many studies to follow and correlations to be developed. His work continued in the general area of heat transfer and in time he became internationally recognized as an authority in heat transfer, distillation, and the flow of viscous liquids. McAdams retired from MIT as a Professor of Chemical Engineering in 1959 due to failing health and passed away in 1975 at the age of 83, leaving a legacy of an eminently distinguished career and transformative contributions to heat and mass transfer that have had a lasting impact on contemporary chemical and mechanical engineering.

Llewellyn M. K. Boelter was born in Winona, Minnesota on August 7, 1898, and obtained his early education in Minnesota and Oregon before moving on to California where he received his college education at the University of California – Berkeley (UC-Berkeley). He received a BS degree from the College of Mechanics in 1917 from UC-Berkeley, and then a MS degree in Electrical Engineering in 1918. The following year in 1919, he began his professional journey in academia when he was appointed as an instructor of electrical engineering at UC-Berkeley. Four years later (1923) he was promoted to Assistant Professor of Experimental Engineering in the Department of Mechanical Engineering (ME) at UC-Berkeley. Boelter was subsequently promoted, in 1927 and 1934, , respectively, to Associate Professor and Professor in ME, and then again, in 1943, was appointed as Associate Dean of Engineering at UC-Berkeley. However, in the subsequent year (1944), he was recruited by the University of California at Los Angeles (UCLA) and he became the founding dean of its College of Engineering. His primary responsibility at the time was to establish this new college, which was subsequently renamed (in 1969) as School of Engineering and Applied Science, and eventually (in 1999) became the Henry Samueli School of Engineering and Applied Science at UCLA⁴. Boelter settled in at UCLA and spent the next 21 years of his academic career (until his retirement in 1965) as Dean of Engineering, the longest tenure of anyone who has served in this capacity, shaping both the engineering curriculum as well as how it was taught. In this period, he was also appointed as a Visiting Professor at Purdue University in 1952.

These were opportune and exciting times as the heat transfer community was growing with many mechanical engineers (besides chemical engineers) actively interested in and engaged with the field. Almost in parallel with the activity on the East Coast of U.S. (spearheaded by McAdams, ChemE), on the West Coast, MEs at UC-Berkeley led by L.M.K. Boelter, and supported by V.H. Cherry and H.A. Johnson, compiled a set of teaching notes in 1932. These heat transfer notes were based largely on the German literature of that time, which reflected much more analytical and theoretical perspectives, and they were used primarily to supplement graduate-level lectures in heat transfer at UC-Berkeley. Shortly after the death of Cherry (1941), the Heat Transfer Notes that were informally issued in 1932–1933, were corrected for errors found by students and others who used them, and published in 1946 by the University of California Press [19] (see Fig. 4 for book cover and table of contents). To fill-in for Cherry, R.C. Martinelli had joined the effort as a fourth author; he had been a student contributor and subsequently an outstanding young professor who died prematurely in 1949 at the age of 35. The important role of Heat Transfer Notes that were used in Boelter's classes to educate and shape the research orientation of engineers of that time, and which were republished by McGraw-Hill in 1965 [42], in the development of heat transfer in U.S. in the 20th century should not be underestimated.

In one of his radiopodcasts⁵ of the series, Engines of Our Ingenuity (the essay version of these was later published as a book in 2000 [43]), John H. Lienhard made the observation that Boelter was a “great teacher” and that “Knowledge was the great equalizer for Boelter.” Most people (faculty, staff, and students alike) around him only used last names with no titles in their interpersonal interactions. When Boelter moved to UCLA in 1944, in his effort to make learning a very high priority, he initially abolished departments (although this approach was later abandoned). The idea was to promote broad general engineering learning, which , for example, also reflected in his teaching assignments; if you taught heat transfer in one quarter, in the following quarter you might be teaching electric circuits. Moreover, he was a vigorous proponent of assigning homework, particularly questions for which he did not know the solutions, so as to inculcate sharp minds and he would quip: “I see no use in giving problems to which I already know the answer.” In 1963, while addressing the freshman class at UCLA, Boelter characteristically made these profound comments [44]:

To mark the 65th birthday of L.M.K. Boelter, a commemorative collection of technical papers and more (Heat Transfer, Thermodynamics, and Education: Boelter Anniversary Volume) was published [51]. Edited by Harold A. Johnson, it had a six-member Editorial Board that included four from UC-Berkeley (E. D. Howe, H. A. Johnson, M. P. O'Brien, and C J. Vogt), and one each from UCLA (H. B. Nottage) and Dartmouth College (M. Tribus). Besides a Preface by the Editorial Board and a two-page biography of Boelter written by Vogt, it had 34 papers on Heat Transfer, Thermodynamics, and Education from a list of 43 contributors. The latter included F. W. Dittus, Robert Drake, Ernst R. G. Eckert, Harold Johnson, Frank Kreith, Herb Nottage, E. F. Romie, Ralph Seban, Myron Tribus, Heinz Popendiek, and many others, who acknowledged the inspiration received from a great educator. According to Johnson, this celebratory volume was conceived and published to honor Boelter for his “integrity, imagination, vision, and compassion, his way of treading softly to avoid hurting others – even those who argued against his ideas.”

In addition to his work in engineering education, heat and transfer, thermodynamics, and other technical areas, Boelter was involved in many volunteer activities that addressed issues such as manufacturing and production, traffic and transportation, illumination, and urban planning. For example, he served as Director of the testing agency for the California Division of Motor Vehicles (1919–1944); Member of the state Board of Registration for Civil and Professional Engineers (1947–1960); Vice President and President of the Los Angeles City Planning Commission from (1954–1962); and as a member of an extraordinary number of municipal and state (15), national (24) and professional (22) boards. In fact, he advocated the application of systems engineering principles to urban and town planning, including transportation, and even made a scholarly contribution [52] to such analyses. After retiring from UCLA in 1965 and his wide spectrum of community activities, L. M. K. Boelter passed away the following year (July 1966), just shy of his 68th birthday, but his influence on heat transfer education and practical engineering research endures to this date. In fact, as a fitting tribute to his work, the second engineering building built during Boelter's tenure as Dean at UCLA is appropriately named Boelter Hall.

The ASME Heat Transfer Division (HTD) was officially formed in 1938 during the Summer Meeting as a working Professional Group, consisting of prominent mechanical and chemical engineers, carved out of the ASME Process Industries Division. However, formal induction of HTD as a separate administrative unit of ASME was delayed until 1941. The formation of a similar grouping (Heat Transfer and Energy Conversion Division, which is now renamed the Transport and Energy Processes Division) in the American Institute of Chemical Engineers (AIChE) ran somewhat behind that of ASME (Knudsen [53]). Note that AIChE was formed in 1908 (28 years after ASME) in order to establish chemical engineering as a professional group, distinct and independent of industrial chemists and mechanical engineers⁶. Nevertheless, many of the active heat transfer participants at that time were chemical engineers, such as McAdams, and they worked closely with mechanical engineers on prevailing heat (and mass) transfer problems of interest. In fact, about one-third of the first 15 Chairs of the ASME HTD were chemical engineers.

It was in this collaborative environment, though by now housed in two distinct organizations (ASME and AIChE) that a joint heat transfer conference was born. The 1st National Heat Transfer Conference was held in 1957 at The Pennsylvania State University, University Park, PA. It was the only one to be organized on a college campus, and was designed to bring mechanical and chemical engineers with a broad range of interest in heat transfer together in a common setting; Kezios [54] has described the events in some detail. It was agreed that AIChE would host the conference on even-numbered years and ASME on odd-numbered years. It would not be held in the year the International Heat Transfer Conference was organized (once in four years). George “Dusie” Dusinberre of Penn State (a witty man who coined many aphorisms that had become department folklore) was in charge of the first national conference. The first conference was dedicated to William H. McAdams to recognize both his classic text, Heat Transmission, and his impending retirement from MIT. Participants stayed in the Nittany Lion Inn, and sessions were held in various buildings across the Campus. Finally, it should be noted that the National Heat Transfer Conference lasted for 44 years⁷, as the participation of AIChE as well as the process and heat-transfer-related industry declined substantially for a variety of reasons. One was the exceedingly large focus in the latter years on “science” and academic research, instead of engineering and processes. Others were the declining engineering membership of AIChE (which began to have more chemistry-oriented members) as well as the emergence of Heat Transfer Research Inc. (HTRI), which focused heavily on practical applications and large physical plants. This problem had also been debated and forewarned in the early days of the conference [44].

To further advance the activities of HTD and recognize members who made significant heat transfer contributions, two major awards were established [44]: Heat Transfer Memorial Award (established in 1959 by ASME, but was first given in 1961 to Novak Zuber), and Max Jacob Memorial Award. The latter was established jointly by ASME and AIChE in 1961 to honor Jakob, after his de-ath in 1955, for his exemplary service as a researcher, educator, and author. Max Jakob was especially remembered for his two-volume Heat Transfer I and II books [20,21], of which the latter was published posthumously with the assistance of S. Peter Kezios. This award is administered jointly by ASME and AIChE, and from 1961 through 1964 the first four recipients were: Ernst R. G. Eckert, Llewellyn M. K. Boelter, William H. McAdams, and Ernst Schmidt. In particular, Professor McAdams, recently retired in 1959, received the 1963 award at the 6th National Heat Transfer Conference. The photograph in Fig. 5 is from the awards ceremony and seen along with McAdams (second from right) are Dean L. M. K. Boelter of UCLA (1962 recipient), Warren M. Rohsenow of MIT, who was Chairman of the conference, and Ronald B. Smith, ASME President at that time. This photo is perhaps one of the few that features both Boelter and McAdams in the same frame! Later in 1988 when the half-century of HTD was celebrated [8], prominent members were honored with the ASME HTD 50th Anniversary Award at the National Heat Transfer Conference held in Houston, TX. A total of 23 living (at that time) along with 5 deceased HTD members (including Llewellyn M. K. Boelter) were honored recipients. However, in retrospect, the omission of William H. McAdams from the list of the (deceased) recipients of the 50th Anniversary Award was very unfortunate.

Nevertheless, in his illustrious career, McAdams received several other awards that included: Honorary Doctor of Science Degree, University of Kentucky (1945), AIChE Presidential Certificate of Merit (1949), AIChE William H. Walker Award (1949), Chair of the MIT Faculty (1947–1949), and he was inducted in the Hall of Distinguished Alumni, University of Kentucky (1965). Likewise, some of the other recognitions for Boelter include the American Society for Engineering Education (ASEE) Benjamin Garver Lamme Award (1956), ASME Medal (1957), Dean of Engineering at UCLA (1944–1965; the longest such tenure at that school), and Honorary Doctor of Laws degree from UCLA (1966). The enduring contributions of these two American pioneers of heat and mass transfer, however, transcend achievement awards and recognitions, for they still have relevance to research and education in the present times. Perhaps a reiteration of this history is needed in order to bring back and reinvigorate the “engineering” in heat transfer “science” so as to address contemporary applications and industry needs.

After the 2020 Summer Heat Transfer Conference, where the Boelter–McAdams centennial celebration lecture was presented⁸, the HTD K-3 Honors and Awards Committee made a proposal⁹ to the ASME HTD to initiate a new award. It was suggested that it be named the Boelter–McAdams Prize, so as to honor the outstanding contributions these two American pioneers had made to the field of heat transfer and mass transfer. This was discussed and approved by the HTD as a biennial award that seeks to recognize and honor the achievements of a midcareer (8–12 years) researcher or engineering practitioner. In keeping with the true spirit of the contributions of the two trail-blazing pioneers, applied engineering aspects of thermal science are particularly emphasized in the achievement qualifications of a nominee. The inaugural award was conferred upon Dr. Subramanyaravi (Ravi) Annapragada, innovation and product development leader at Carrier Corporation at the Summer Heat Transfer Conference, Washington, DC, July 10–12, 2023. He was recognized for his contributions to the “fundamental understanding of thermal sciences within sustainable heating, cooling, and dehumidification technologies, in particular, thermo-electrics and caloric-material-based heat pumps, leading to the development of novel, compact, sustainable products.”

The truly transformational contributions of both Boelter and McAdams to heat and mass transfer research, education, and practice, are further articulated in the laudatory comments by former students and colleagues of their time. One characteristic perspective is that of Darrel Sager, a long-time Hughes Aircraft Company employee and now a retiree, who had attended UCLA and received his BSE degree in June 1959 when Dean Boelter addressed that year's senior class. The 1950s decade was an exciting one for engineers. Sputnik had just been launched (October 4, 1957) and the UCLA engineering department had just obtained a digital computer – all within a short time before Boelter retired. Darrel distinctly remembers [55] that Boelter strongly encouraged BS engineering graduates to obtain a “generalist” degree with a broad range of courses, and if a more specific degree was desired, an MS in engineering was next. After 43-some years and based on personal experience at Hughes Aircraft, he endorsed Boelter's views on taking a spectrum of courses during undergraduate engineering: “… he was absolutely correct!”

Another laudatory articulation comes from the Late Professor Frank Kreith (1922–2018), who was Boelter's last MS student (1955) at UCLA and later taught at UC-Berkeley, Lehigh University, and University of Colorado – Boulder [56]. He compared the contributions of Boelter and McAdams with the comments [57], “The difference between the East Coast and the West Coast may be seen by comparing Boelter's Heat Transfer Notes and McAdam's Heat Transmission. The notes relied heavily on differential equations and mathematics to obtain solutions while McAdams relied on insight and experimental correlations. However, when I began to prepare a book on heat transfer, I realized just how complementary those two approaches were.” Kreith's tribute [57] to Dean Boelter is quite insightful and it summarizes commendatory comments from Warren Giedt, Heinz Poppendiek, Myron Tribus, and several other peers in that period. In fact, perhaps the first comprehensive textbook on heat transfer for ME and ChE undergraduate students (as well as a rising graduate student reference book) was published by Frank Kreith in 1958 [26]. That classic book was indeed based on the seminal works of both Boelter and McAdams, and it is now in its eighth edition¹⁰ [11,58,59].

One of the foremost German immigrant influencers of heat transfer development in the U.S. was Professor Ernst R. G. Eckert (1904–2004), University of Minnesota [60]; he moved to the U.S. from Germany in 1945 as part of “Action Paperclip.” In his erudite celebratory article [15] on the 100th anniversary of the founding of ASME, he articulated the extensive developments during the five decades of 1930–1980 in the broad field of heat transfer. Highlighting the primary growth drivers of that period, he especially pointed out the roles of both McAdams and Boelter as follows:

Another major interlocutor and influencer of heat transfer research and engineering education of that era was Professor Myron Tribus (1921–2016), UCLA, Dartmouth, and MIT [61]. In chronicling the history of the ASME HTD [44], Layton and Lienhard have attributed the following quote to Tribus and his 1971 lecture during the L.M.K. Boelter Library dedication at Purdue University:

Many dedicated educators and researchers contributed to making heat (and mass) transfer a field of engineering study and research in the U.S. to what it is today. However, in the 20th century, two quintessential American pioneers, L.M.K. Boelter and W.H. McAdams, played a very special and transforming role in revolutionizing the field of heat transfer. Both men were exceptionally talented and both helped to stimulate major advances in this field. It should be noted that neither Boelter nor McAdams had an earned Ph.D. and both began their academic teaching and research careers in 1919! They stimulated people in industry, academia, and government to think about familiar as well as challenging problems in new ways. In academia, Boelter and McAdams impacted faculty members and students in not only the developing trajectory of the engineering curriculum that bridged chemical and mechanical engineering but path-breaking research as well and helped open new doors in many ways.

Born in the central part of the country but spanning the coastal boundaries, McAdams, a Chemical Engineer on the East Coast, and, Boelter, a Mechanical Engineer on the West Coast, had a monumental impact on the field of heat transfer in the U.S. and around the world. The 100th anniversary of the university teaching and research careers of these two very talented individuals was celebrated in 2019. In the archival annals of heat transfer, the contributions of Llewellen Michael Kraus Boelter and William Henry McAdams will never be forgotten. They will be fondly remembered as two very exceptional researchers and educators, but with somewhat different perspectives, who played an essential and foundational role in the contemporary field of heat (and mass) transfer.

The authors attest that all data for this study are included in the paper.